Social cohesion: group sizes and the duration of bonds

From solitude to the mega-society

From the sperm whale, solitary during its dives, to the mega-group of 1,000 common dolphins, cetaceans display the full range of social structures. The multi-level alliances of the common bottlenose dolphins of Shark Bay last more than 20 years, and sperm whale matrilineal units persist across generations. This comparison tool presents documented group sizes and the longevity of social bonds.

Matrilineal societies and male alliances: the known models

Cetacean societies are organised along three broad models. The first is the stable matriline: in the resident killer whale of the North-East Pacific, individuals stay with their mother all their lives, forming pods of 10 to 60 animals that share a single vocal dialect. The sperm whale follows a similar pattern, with female social units of 10-12 individuals that endure over decades (Whitehead).

The second model is the multi-level male alliance documented by Richard Connor at Shark Bay (Australia) in the common bottlenose dolphin: 2-3 males ally to control females, then 4-14 males form super-alliances. The third is the fission-fusion society: groups come together and disperse with the rhythm of resources, as in the common dolphin and the striped dolphin in the Mediterranean.

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